VITAMIN
E
No
other vitamin has attracted as much attention from
both basic scientists and clinical scientists over
the past decade as vitamin E. Interest grew as researchers
learned that oxidative damage to vital tissues plays
an important role in the development of many chronic
diseases and in the aging process. The presence of
vitamin E in cell membranes helps protect the cell
because it serves as a fat-soluble free-radical scavenger
and antioxidant. It works hand in hand with the other
antioxidant vitamins and compounds in the body. And
it explains the role of antioxidant vitamins and evidence
for their usefulness in maintaining good health. This
section summarizes the properties of vitamin E.
FUNCTION
Vitamin
E sits in cell membranes, and its primary function
is as a biological antioxidant and cell membrane protector.
Oxygen is life-giving, but it can also be harmful.
One of the most potentially damaging reaction involving
oxygen is with unsaturated fatty acids. Free radicals
generated during normal metabolic reactions in which
oxygen is involved can react with unsaturated fatty
acids in cell membranes to form substances called
organic peroxides. Organic peroxides are toxic to
cells because they can take part in a chain reaction
with other neighboring fatty acids, eventually destroying
the cell. Without vitamin E and other antioxidant
vitamins, oxygen can, in effect, convert fluidlike
unsaturated fatty acids to inactive solids, rendering
them unable to function. The body has several other
antioxidants and free- radical- scavenging compounds
that back up and complement the action of vitamin
E after it has been inactivated by picking up a free
radical.
There is a ample research on this role for vitamin
E. For instance, people who eat more polyunsaturated
fat in their diet need more vitamin E to prevent cellular
damage. Relatively little vitamin E in the diet may
lead to the deposition of oxidized fats in tissues.
That is not to say that vitamin E can stop the aging
process; it cannot. But it is possible that vitamin
E deficiency may speed the aging of essential tissues.
Unless free radicals are quenched, they can react
with blood fats, setting up an inflammatory process
associated with atherosclerosis that leads to the
formation of blood clots, and possibly heart attack.
A free-radical attack on the cell nucleus can result
in mutations that could lead to cancer. Low vitamin
E intake has been associated with a higher risk of
heart disease and cancer. Thus vitamin E's main function
is unlike most other vitamins in that it does not
participate in biochemical reactions. Rather, vitamin
E simply acts as a sponge to soak up damaging free
radicals.
DAILY
REQUIREMENTS
The
strength of vitamin E was originally based on measures
of biological activity and expressed in international
units (IU), and different forms of the vitamin have
slightly different IU equivalents.
In human nutrition, the most important form of vitamin
E is alpha tocopherol, and the natural form of this
substance is d-alpha tocopherol. It has strength of
1.5 IU per mg. Synthetic alpha tocopherol, d1-alpha
tocopherol, come in two types: d1-alpha tocopheryl
acetate has a strength of IU per mg, and d1-alpha
tocopherol has a strength of 1.1 IU per mg. In 1980
the RDA for vitamin E was changed from IUs to d-alpha
tocopherol equivalents (TE). One TE is mg of d-alpha
tocopherol and also to 1.5 IU. Vitamin products still
use IU to express the amount of contained vitamin
E. Nutrition tables have switched to TE values, however.
Based on early studies, an RDA of 30 IU of vitamin
E per day was set in 1968. In 1974 the National Research
Council reduced the RDA to 10 TE for adult males and
8 TE for adult females on the basis of dietary surveys
that revealed that most diets contained between 10
and 15 IU per day. The RDA value has not been altered
since 1974. Since there were no obvious sign of vitamin
E deficiency in the United States, it was assumed
that the previous recommendation was too high. This
decision was extremely controversial. On one hand,
there was no evidence that 15 IU per day would not
satisfy human needs for the vitamin. On the other
hand, emerging knowledge of the important role vitamin
E plays in removing damaging free-radical compounds
in the cells suggests to many that more, not less,
vitamin E is needed for optimal health. Since vitamin
E is nontoxic, it is not unreasonable to push for
higher intakes. This controversy is still not settled.
While it would be difficult to get more that 30 IU
from food, it seems prudent to increase our consumption
of whole grains and unprocessed foods to increase
vitamin E intake. Vitamin E supplements may be warranted
as discussed in "Antioxidant Vitamins".
DIETARY
SOURCES
The
tocopherols are made by plants, probably as protection
against oxidation of other vital fatty acids. Animals
pick up their tocopherols from plant sources and use
them as protection from the adverse effects of oxygen.
There are more than six tocopherols found in plants,
but alpha-tocopherol is the most potent. Unlike vitamins
A and D, which are stored only in body fat and the
liver, vitamin E is found in all body tissues in the
cell membranes, so it is present in meats, but in
rather low amounts. Over 60 percent of the dietary
vitamin E consumed in the United States comes from
plants, especially from corn or cottonseed oil, green
vegetables, and wheat germ. Other good sources are
listed in the accompanying table.
Vitamin E is destroyed in the presence of oxygen and
heat. Thus the vitamin E content of foods variety
widely depending on how they were handled during processing
and storage. Prolonged freezing of vitamin E - containing
foods will destroy vitamin E content unless care is
taken to prevent exposure to air. Eating uncooked
fresh fruits and vegetables will help increase vitamin
E intake.
Vitamin
E Content of Selected Foods
(Average adult RDA is 10 TE, or 15 IU)
|
Food
|
Approximate
content
(IU per 3 oz.)
|
| Almonds |
13.5
|
| Almond
oil |
5.8
|
| Apricot
oil |
19.0
|
| Brazil
nuts |
5.9
|
| Cabbage |
6.4
|
| Cashew
nuts |
4.6
|
| Corn
oil |
19.0
|
| Cottonseed
oil |
40.0
|
| Hazelnuts |
19.0
|
| Margarine
|
16.2
|
| Peanuts |
6.3
|
| Peanut
oil |
14.4
|
| Safflower
nuts |
31.5
|
| Sunflower
seeds |
28.0
|
| Walnuts |
20.0
|
| Wheat
germ |
144.0
|
| Whole
wheat flour |
27.0
|
DEFICIENCIES
Most
vitamin E deficiency signs and symptoms are related
to oxidative damage to cell components. One perplexing
point is that while a vitamin E - deficient diet is
life-threatening to animals, humans are not affected
as severely. Vitamin E - deficient animals develop
sterility, liver damage, muscular dystrophy, heart
degeneration, and anemia, but no such vitamin E deficiency
symptoms exist for humans. Part of the reason for
the difference may be that vitamin E is widespread
in our diets and that we have some reserves stored
in our body fat.
A true human vitamin E deficiency state was not discovered
until the 1960s, when a group of premature infants
was accidentally given formula with no vitamin E.
The infants became anemic and developed edema that
responded to vitamin E treatments. In Illinois, a
group of volunteers was given a diet with low levels
of vitamin E. These studies showed that red blood
cells from normal individuals survived longer than
cells from those who were vitamin E-deficient. There
were no other obvious deficiency signs in the volunteers.
The findings of this study, which originally set out
to determine how much vitamin E would be needed to
return the volunteer's red blood cells to normal,
led to the 1968 recommendation by the Food and Nutrition
Board to set the RDA at 30 IU of vitamin E.
Patients who have a problem absorbing and digesting
dietary fats may with the time develop a vitamin E
deficiency. People with bile problems have difficulty
absorbing fats, as to premature infants and cystic
fibrosis patients. After several years, signs of nerve
damage being to appear, leading to loss of reflexes,
loss of sensation, muscles weakness, problems with
eye movement, and difficulty with balance and coordination.
If the vitamin E deficiency is not corrected, the
damage may be irreversible.
Because of the high susceptibility of the red blood
cell membranes to oxygen damage, hemolysis may occur
in people deficient in vitamin E. Patients with inherited
conditions that predispose them to oxidative stress,
such as glucose-6-phosphate dehydrogenase (G6PD) deficiency,
are prone to vitamin E deficiency. Iron is a pro-oxidant
that can place an increased demand on vitamin E stores.
Patients taking an iron-containing product or those
who have trouble eliminating iron from their body
should take vitamin E supplements.
TOXICITY
There
are no major side effects associated with vitamin
E; it is remarkably nontoxic.
One of the best evaluations of vitamin E toxicity
was conducted at the National Institutes of Health.
Twenty-eight institute employees voluntarily took
doses ranging between 100 and 800 IU a day for an
average of three years. A battery to tests designed
to uncover possible toxic effects was performed on
each volunteer, and none was found. There are a few
reports in the medical literature describing possible
stomach upset, diarrhea, dizziness, and increased
blood-clotting time with high doses of the vitamin,
but most agree that vitamin E is nontoxic in doses
below 800 IU per day.
INTERACTIONS
Vitamin
E facilitates the absorption, tissue storage, and
utilization of vitamin A. People who must take vitamin
A to correct a deficiency should also take vitamin
E. However, in huge doses, vitamin E can actually
slow the absorption of vitamins A and K from the gastrointestinal
tract.
Vitamin E can also inhibit formation of the active
forms of vitamin K, thereby inhibiting the ability
of blood to clot. It can also inhibit the ability
of blood platelets to aggregate. This may be beneficial,
for less-sticky platelets theoretically confer a reduction
in the risk of stroke, blood clots in the lungs, and
heart attacks.
Vitamin E supplements should probably not be used
in doses larger than 50 IU per day by people taking
anticoagulant drugs, aspirin or similar drugs with
an effect on platelets, or those with blood-clotting
disorders.
THERAPEUTIC
USES
Vitamin
E is perhaps the most important of the protective
antioxidant and free-radical-scavenging compounds
in the body. It has a clear role in protecting the
body against the damaging effects of oxygen. Higher
intakes lower the risk for heart disease and cancer.
This aspect of vitamin E is covered in "Antioxidant
Vitamins". Below are listed some other uses for
vitamin E based on the ability of this vitamin to
act as a fat soluble free-radical scavenger and antioxidant.
- Reduce
environmental hazards such as ozone, nitrogen dioxide,
and cigarette smoke. Increasing levels of pollutants
in our atmosphere can lead to adverse health effects
because these components are reactive and cause
free-radical oxidative change. Some suggest that
people who live in areas with air pollution problems
should increase their intake of antioxidant vitamins,
especially vitamin E.
- Reduce
cardiac toxicity of the anticancer drugs daunorubicin
and doxorubicin. These drugs are toxic to the heart
muscle because they promote the formation of free-radical
intermediates. Vitamin E supplements have been shown
to reduce this damage.
- Treat
hemolytic anemia associated with hereditary deficiencies
of the enzymes known as G6PD and gluathione peroxidase.
Both of these conditions can lead to excess oxidation
and consequent damage to body tissues. Vitamin E
supplements have been shown to reduce breakdown
of red blood cells in people with these disorders.
- Relieve
PMS symptoms. There are several small studies indicating
that a supplement of 400 IU per day of vitamin E
may reduce some symptoms of premenstural syndrome.
Vitamin E can modulate prostaglandin synthesis through
its antioxidant action, and this may be a possible
mechanism of action here.
- Relieve
intermittent serve leg muscle pains (intermittent
claudication). Intermittent claudication is characterized
by attacks of lameness and pain brought on by walking.
The pain comes from arteriosclerosis in the blood
vessels of the legs; the reduced blood flow means
that the calf and buttock muscles receive insufficient
oxygen. Several studies have evaluated the usefulness
of vitamin E in this condition by measuring the
exercise tolerance of patients receiving the vitamin
compared with patients who received traditional
treatment and others receiving no treatment at all.
By all criteria, vitamin E in doses over 400 IU
per day was shown to be of some benefit after six
months of continuous use.
- Relieve
nighttime leg cramps. There is limited evidence
that vitamin E might offer some benefit to those
who suffer from this annoying affliction, but controlled
studies on the effectiveness of vitamin E for this
problem are lacking. One study showed that a dose
of 400 IU, taken before bed, was effective in reducing
the frequency and severity of attacks.
- Speed
healing of wounds and clearing of scars. Although
this use of vitamin E has not been thoroughly tested,
many people claim to have experienced great benefit
from applying vitamin E creams or the oil from vitamin
E capsules directly to wounds and scars. Vitamin
E cream is a cosmetically elegant, more expensive
way of applying the vitamin to your skin that simply
using the oil from a vitamin E capsule, which can
be removed by puncturing the capsule with a pin
and squeezing the oil out. Either form of the vitamin
should be applied to the wound to scar two or three
times a day. Presumably vitamin E is working as
an antioxidant and free-radical scavenger in preventing
further damage to the tender new tissue being formed
during the healing process, although this has not
been proven. If so, the vitamin would presumably
work best when applied to a wound that has closed
and is starting to heal. There are few adverse effects
to this remedy, as long as you don't rub the cream
or oil directly into an open wound. If you have
a stubborn wound that is not healing as fast as
you would like, this controversial treatment may
be worth a try. But you should remember that a sore
that doesn't heal may be warning sing of cancer
or another serious medical problem, so get medical
attention if you have any doubts.
- Decrease
platelet aggregation. Aggregation of blood platelets
is part of the process of blood clot formation,
but an increased tendency to platelet aggregation
is dangerous because of the risk for the formation
of unwanted clots, leading of strokes and heart
attacks. Vitamin E can decrease the aggregation
of platelets in doses of greater than 200 IU per
day. While this is generally beneficial, you should
not take vitamin E if you have blood-clotting problems
or are taking "blood thinners" such as
warfarin.
- Alleviate
deficiencies in cystic fibrosis patients. Individuals
with cystic fibrosis do not absorb fats, and they
show deficiencies of the fat-soluble vitamins, especially
vitamin E. Doses of 200 IU per day or more are needed.
- Reduce
risk of cataracts. Studies have shown that people
who take vitamin E supplements have a lower risk
of cataract formation. Lipid peroxidation may be
part of the process of the formation of cataracts.
More studies are needed to define the optimal doses
and the extent of their benefit, but vitamin E supplements
may be beneficial for this and many other degenerative
conditions in the elderly.
- Benefit
people who engage in heavy exercise. Vitamin E has
long been used by athletes in the hope of improved
performance. Strenuous exercise has been shown to
result in increased lipid peroxidation and free-radical
damage in muscle tissue. Most studies on vitamin
E and exercise have been done in animals; careful
studies on student athletes in England and on members
of a college swimming team in Louisiana have shown
that vitamin E did not help, but studies with high-altitude
mountain climbers indicated that vitamin E supplements
have some benefits compared to placebo. More work
is needed in this area.
- Reduce
tardive dyskinesia. Tardive dyskinesia is a side
effect of antipsychotic drugs. It is characterized
by involuntary head movements and may be a consequence
of free-radical damage to nerves. Small studies
have shown that vitamin E in very high doses helps
reduce these movements.
- §
Protect premature infants. Premature infants have
a low capacity for protection against oxidative
damage. Vitamin E is sometime supplemented to prevent
damage to their lungs and eyes. Earlier use of a
vitamin E injection product resulted in some deaths
associated with the product, and most supplementation
now is given orally.
- Prevent
cancer, heart disease, atherosclerosis, and decreased
immune function. The application of vitamin E supplements
in the prevention of these diseases is considered
in " Antioxidant Vitamins"
- Slow
the progression of Alzheimer's disease. A well designed
study showed that high dose vitamin E slowed the
progression of Alzheimer's as well as did a drug
called selegiline, a standard treatment. While this
study does not represent a major breakthrough, this
benign vitamin may help people with Alzheimer's
and their families. Further study may reveal other
uses in mental degeneration.
UNSUBSTANTIATED
CLAIMS
Treatment
of cystic breast disease
Noncancerous
breast lumps affect millions of American women. Early
studies indicating benefit with vitamin E have not
been substantiated.
Treatment
of angina
While
vitamin E has a role in the prevention of heart disease
and the prevention of further heart attacks after
the first, it does not seem to be of help in treating
angina.
Improvement
of sexual function
Sorry
- despite its reputation, vitamin E will not do anything
for your sexual prowess. A Canadian evaluation could
not demonstrate any effect of vitamin E on the sexual
activities of couples when compared with a group receiving
a placebo.
Vitamin E has also been promoted for other uses for
which its value has not been proven. We cannot recommend
that you take this vitamin to treat acne, allergies,
anemia, arthritis, athlete's foot, backache, baldness,
bedsores, boils, bronchitis, bursitis, colitis, the
common cold, constipation, cystitis, dandruff, diabetes,
emphysema, eyestrain, fatigue, fluid retention, gallstones,
gout, hay fever, headache, hemorrhoids, impetigo,
impotence, infertility, kidney stones, loss of vision
measles, Meniere's disease, menstrual cramps, mental
illness, multiple sclerosis, muscular dystrophy, nephritis,
night blindness, obesity, osteoporosis, Parkinson's
disease, phlebitis, prostatitis, sciatica, sinusitis,
sunburn, thyroid disease, ulcers, vaginitis, or warts.
AVAILABILITY
Another
controversial point about vitamin E is the merit of
using the natural form, d-alpha tocopherol, versus
either of the synthetic forms, d1-alpha tocopherol
or d1-alpha tocopherl acetate. Most common vitamin
products contain synthetic vitamin E. However, the
natural d-alpha tocopherol seems to bind better with
one of the proteins that help move vitamin E into
and within the cell. The implications of this observation
are that with equal amounts of synthetic or natural
vitamin E, the natural would be better-utilized. Since
generic natural vitamin E is readily available and
not much more expensive than the synthetic kind, we
recommend purchase of the natural product. But be
careful : Some brands have Nature or Natural as part
of the brand name, thus giving the consumer the impression
that vitamin E in the bottle is the natural kind.
But unless the product label says it is d-alpha tocopherol,
the vitamin E is synthetic. The "semisynthetic"
d-alpha tocopheryl acetate is recommended also. The
acetate group confers stability to the molecule and
is readily removed by enzymes in the intestine, thereby
releasing the d-alpha tocopherol.
Recently some vitamin E products have appeared on
the shelves labeled as all natural vitamin E, but
close examination of the label reveals that the capsules
contain a mixture of natural d-alpha tocopherol and
synthetic d1-alpha tocopherol. These products are
basically mislabeled and should be avoided. If you
want to take the all natural vitamin E, demand a product
that is 100 percent d-alpha tocopherol. Some natural
vitamin E products contain "mixed tocopherol".
These products contain a mixture of tocopherols obtained
from the plant source. As far as we know, 40 0IU of
mixed natural tocopherols is a beneficial as 400 IU
of d-alpha tocopherol. The knowledgeable consumer
can make a good choice in purchasing dietary supplements,
but it will require careful scrutiny of the label.
When in doubt, ask you pharmacist for assistance.
Another product is micronized or emulsified vitamin
E. These products are water-soluble because the vitamin
has been dispersed into fine droplets in water. For
those with fat-absorption problems, it may be worthwhile
to use these water soluble products because they do
not need to be absorbed like fats.
Capsules and tablets of vitamin E are available without
a prescription in strengths ranging from 200 to 1,000
IU. The concentration in multivitamin products is
usually 30 IU. Vitamin E ointments, lotions, and creams
are also available without a prescription. The usual
concentration of vitamin E in these products is 30
IU per gram.
